JP2002317709A - Failure diagnostic device for evaporative emission purge system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a failure diagnosis near a pressure control range by a pressure control valve(PCV) at low cost due to elimination of a fuel temperature sensor and without an influence of an outside air temperature and a fuel remaining level. SOLUTION: When an engine is started and a pressure P in a fuel tank (internal tank pressure) reaches a diagnosis start pressure P1, a diagnosis execution condition satisfaction flag is set to start a failure diagnosis (S5). A succeeding elapsed time is then measured, and when a preset timer setting time is reached, the diagnosis execution condition satisfaction flag is cleared to stop the failure diagnosis. The diagnosis start pressure P1 is set slightly lower than the pressure control range by the PCV interposed in an evaporative emission passage interconnecting the fuel tank and a canister, so that the failure diagnosis can be started before actuation of the PCV. The PCV is opened at the failure diagnosis start, and the diagnosis monitors a change in the internal tank pressure P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis apparatus for an evaporative purge system that determines whether a condition for performing diagnosis is satisfied based on the pressure in a fuel tank.

[0002]

2. Description of the Related Art Evaporated fuel (evaporation gas) generated in a fuel tank while an engine is stopped is adsorbed in a canister, a purge passage is opened under predetermined operating conditions after the engine is started, and an intake pipe negative pressure is reduced. Utilizing it, the fuel particles adsorbed in the canister are desorbed and led to the intake system,
Evaporative purge systems for combustion are known.

[0003] Further, in the evaporative purge system, if a leak hole is opened in the middle of the flow path from the fuel tank to the intake pipe, or if the seal at the joint of the pipe is deteriorated, the evaporated fuel is removed from these locations. Since it is released into the atmosphere, a failure diagnosis device that checks for the presence or absence of a leak is also provided.

[0004] Generally, in the failure diagnosis of the evaporative purge system, the presence or absence of a leak is detected by examining the pressure change at that time by defining the flow path from the fuel tank to the intake pipe as a closed space. In this case, there is known a technique for performing a failure diagnosis of an evaporative purge system using an internal pressure sensor provided in a fuel tank.

However, when a failure is diagnosed based on a change in pressure detected by an internal pressure sensor provided in the fuel tank, if the amount of evaporative fuel generated is excessive, a closed space from the fuel tank to the intake pipe due to the evaporative fuel. There is a possibility that the internal pressure will rise and cause an erroneous determination. Therefore, for example, Japanese Patent Application Laid-Open No. 8-296509 discloses a technique for monitoring a fuel temperature in a fuel tank and performing a failure diagnosis only when the fuel temperature is equal to or lower than a predetermined value, thereby preventing erroneous determination. .

[0006] Japanese Patent No. 2699774 discloses a technique of monitoring the time after a cold start and performing a failure diagnosis only in a time range in which fuel evaporation hardly occurs after the cold start.

[0007]

However, Japanese Patent Application Laid-Open No. Hei 8-2
In the technique disclosed in Japanese Patent Application Publication No. 96509, a temperature sensor for detecting the fuel temperature must be provided in the fuel tank, so that the number of parts increases and the product cost increases.

The technique disclosed in Japanese Patent No. 2699774 does not need to detect the fuel temperature.
Although it is not necessary to provide a temperature sensor, the rate of increase in the fuel temperature varies depending on the outside air temperature and the remaining amount of fuel, so that the amount of fuel evaporation cannot be detected accurately, and a highly accurate diagnosis result cannot be obtained. .

In some cases, the internal pressure of the fuel tank is regulated to a predetermined pressure (positive pressure) using a pressure regulating valve (PCV). FIG. 3 shows the relationship between the fuel vapor generation amount and the tank internal pressure after the start in this case. As shown in the figure, in an area A where the amount of generated fuel is small, the tank internal pressure P gradually increases, and in an area B where the amount of generated fuel is medium, PCV is used.
Control operation, the tank internal pressure P becomes a predetermined reference control pressure P
The pressure is adjusted so as to fall within the range o, and thereafter, when the amount of evaporated fuel increases and exceeds the set flow rate of the PCV, as shown in a region C, the pressure in the tank exceeds the control pressure of the PCV and rises.

Normally, when the failure diagnosis is performed in the region A in which the PCV does not operate, the set pressure in the region A easily exceeds, so that the frequency of the failure diagnosis is reduced.
On the other hand, when the execution area of the failure diagnosis is set to the area C, there is a problem that an accurate diagnosis result cannot be obtained because the amount of generated fuel vapor is excessive.

When performing a failure diagnosis in the region A or the region C, the tank internal pressure P increases with an increase in the amount of evaporative fuel generated. It is possible, but in region B, PCV
, The tank internal pressure P is regulated, so that it is difficult to determine the start condition of the failure diagnosis based on the tank internal pressure P.

In view of the above circumstances, the present invention starts a failure diagnosis near the pressure regulation region by the PCV without requiring a fuel temperature sensor, at low cost, and without being affected by the outside air temperature or the remaining fuel amount. Can increase the frequency of diagnosis,
It is an object of the present invention to provide a failure diagnosis device for an evaporation purge system capable of obtaining a highly accurate diagnosis result.

[0013]

In order to achieve the above object, the present invention provides an evaporative fuel passage for guiding evaporative fuel stagnating in an upper space in a fuel tank to a canister, and a purge passage for communicating the canister with an engine intake system. Purge control means for opening and closing the purge passage, tank internal pressure detection means for detecting a pressure in the fuel tank, and a tank internal pressure detected by the tank internal pressure detection means interposed in the fuel vapor passage. Failure diagnosis of an evaporative purge system comprising: pressure adjustment means for adjusting the pressure in the fuel tank to a reference control pressure; and diagnosis execution condition determination means for checking whether a failure diagnosis execution condition is satisfied based on an operation state. In the apparatus, the diagnosis execution condition determination means may be configured to perform a diagnosis when the pressure in the fuel tank reaches a diagnosis start pressure lower than the reference control pressure. And judging that the execution condition satisfied.

In such a configuration, when the engine is started, the fuel stored in the fuel tank circulates and the fuel temperature gradually rises, so that the amount of evaporative fuel gradually increases. At this time, the pressure regulating valve interposed in the evaporative fuel passage is kept closed until the pressure reaches the reference control pressure. Therefore, the tank internal pressure increases substantially in proportion to the increase in the amount of evaporative fuel generated. When the tank internal pressure reaches a diagnosis start pressure slightly lower than the reference control pressure, it is determined that the diagnosis execution condition is satisfied, and the failure diagnosis of the evaporative purge system is started. When the failure diagnosis is started, the pressure adjusting means is opened,
The pressure change of the evaporative purge system is monitored by the tank internal pressure detecting means.

In this case, preferably, the diagnosis execution condition determination means stops the failure diagnosis when an elapsed time after the determination that the diagnosis execution condition is satisfied reaches a set time.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall configuration diagram of the evaporation purge system. In FIG. 1, reference numeral 1 denotes an engine. An intake passage 2 and an exhaust passage 3 communicate with an intake port 1a and an exhaust port 1b of the engine 1, respectively. Intake passage 2
, An air cleaner 4 is provided, a throttle valve 5 is provided downstream thereof, and an injector 6 is provided immediately upstream of the intake port 1a. A catalyst 7 is interposed in the middle of the exhaust passage 3 and communicates with an exhaust muffler (not shown). Reference numeral 8 denotes an intake air amount sensor, 9 denotes a throttle opening sensor, and 10 denotes an O2 sensor.

Reference numeral 11 denotes a fuel tank. The fuel stored in the fuel tank 11 is communicated with the injector 6 via a fuel passage (not shown), and the fuel is metered into the combustion chamber from the injector 6 in a predetermined manner. The surplus fuel is injected into the fuel tank 11 at a predetermined timing.

An internal pressure sensor 12 communicates with an upper space 11a of the fuel tank 11. This internal pressure sensor 12
This is a kind of strain gauge that measures a differential pressure (relative pressure) between the upper space 11a of the fuel tank 11 and the atmospheric pressure. Further, the fuel tank 11 is communicated with a canister 14 via an evaporative fuel passage (hereinafter, abbreviated as “evaporation passage”) 13, and a pressure regulating valve (hereinafter, abbreviated as “PCV”) as pressure control means is connected to the evaporation passage 13. 15 are interposed.

Activated carbon 14a as an adsorbent is provided in the canister 14, and an atmosphere opening port 14b which opens to the outside is formed. A drain valve 16 and a drain filter 17 are interposed in the atmosphere opening port 14b from the upstream side. This drain valve 16 is a normally open type,
The valve closing operation is performed at the time of failure diagnosis to be described later. Further, the canister 14 and the intake passage 2 downstream of the throttle valve 5 communicate with each other via a purge passage 19.
Is provided with a purge control valve 20. The opening and closing operations of the PCV 15, the drain valve 16, and the purge control valve 20 are controlled by an electronic control unit (ECU) 21.

The electronic control unit 21 determines the tank internal pressure P based on a tank internal pressure P [Pa] (relative pressure) detected by the internal pressure sensor 12 after the engine is started. Pa]), the PCV 15 is opened and closed. That is, as shown in FIG. 3, the tank internal pressure P is equal to the positive pressure upper limit value (for example, 1000
[Pa]), the valve closed state is maintained in the area A,
Thereafter, the tank internal pressure P is increased to the positive pressure upper limit value (for example, 1000 [P
a)) When the above is reached, the valve is opened to supply the evaporated fuel in the fuel tank 11 to the canister 14, and the activated carbon 14a adsorbs the fuel particles in the evaporated fuel. When the tank internal pressure P becomes equal to or lower than the positive pressure lower limit value (700 [Pa]), the valve closing operation is performed, so that the inside of the fuel tank 11 is controlled to the reference control pressure Po.
(Region B in FIG. 3). The area C corresponds to PCV1
5 shows a case where the amount of fuel vapor generation is larger than the set flow rate of No. 5, and in such a case, the tank internal pressure P rises beyond the control pressure of the PCV 15.

Further, the electronic control unit 21 executes the evaporative purge control at predetermined intervals after the engine is started. In the evaporative purge control, first, it is determined whether or not the evaporative purge condition is satisfied based on the operating conditions. When the evaporative purge condition is satisfied, a valve opening signal is output to the purge control valve 20 to perform the valve opening operation. Then, the negative pressure downstream of the throttle valve 5 is taken into the canister 14, and the fuel particles adsorbed on the activated carbon 14a are released by the air introduced from the atmosphere opening port 14b, and the purge gas containing the released fuel particles is released. The air is sucked into the intake passage 2 downstream of the throttle valve 5 through the purge passage 19, sent into the combustion chamber, and subjected to combustion processing.

Further, in the electronic control unit 21, after the engine is started, the failure diagnosis of the evaporative purge system is performed about once. In this case, prior to the failure diagnosis of the evaporative purge system, it is determined whether the diagnosis execution condition is satisfied.

The diagnosis execution condition is that a predetermined diagnosis start pressure P is set when the tank internal pressure P is slightly lower than the reference control pressure Po.
1 (approximately 600 [Pa]). When the tank internal pressure P reaches the diagnosis start pressure P1, it is determined that the diagnosis execution condition is satisfied. When the set time is reached after the diagnosis execution condition is satisfied, it is determined that the diagnosis execution condition is not satisfied.

The diagnosis execution condition determination is specifically performed according to a diagnosis execution condition determination routine shown in FIG.

This routine is started at set intervals after the ignition switch is turned on.
To compare the tank internal pressure P with the diagnosis start pressure P1.

For example, in a cold start, since the temperature of the fuel stored in the fuel tank 11 immediately after the start of the engine is the same as the outside air temperature, the amount of evaporative fuel generated is small, and it is determined that P <P1. Then, the elapsed time measurement timer is cleared and the routine ends.

Next, when the fuel temperature gradually rises due to the fuel circulation after the start, the amount of evaporative fuel generation gradually increases and the tank internal pressure P also gradually rises as shown in a region A of FIG. Then, when the tank internal pressure P reaches the diagnosis start pressure P1 (P ≧ P1), the process proceeds from step S1 to step S3, the elapsed time measurement timer is incremented, and the process proceeds to step S4.

The diagnosis start pressure P1 is a value set in consideration of the fluctuation of the tank internal pressure P due to the control operation of the PCV 15, and is a value slightly lower than the reference control pressure P0 (about 600 [Pa] in the present embodiment). ) Is set to Therefore, when the tank internal pressure P reaches the diagnosis start pressure P1, the PCV 15
Is still in a non-operating state, and the internal pressure sensor 12 can detect an increase in the tank internal pressure P that is substantially proportional to the amount of fuel vapor generated. Therefore, even if the rate of increase of the fuel temperature varies depending on the outside air temperature and the remaining amount of fuel, the accurate amount of fuel vapor generation can be detected based on the tank internal pressure P.

Next, when the operation proceeds to step S4, the value of the elapsed time measurement timer is checked. If the elapsed time is within the timer set time, the operation proceeds to step S5, where a diagnosis execution condition satisfaction flag is set and the routine exits. The timer setting time is a time period during which the failure diagnosis can be completed before the tank internal pressure P reaches the region C even if the fuel evaporation amount increases in the normal operation, and is obtained in advance from experiments or the like.

When the value of the elapsed time measurement timer has reached the timer set time, the flow branches to step S6 to clear the diagnosis execution condition satisfaction flag and exit the routine.

The value of the diagnosis execution condition satisfaction flag is read during execution of the failure diagnosis routine, and when the diagnosis execution condition satisfaction flag is set, the failure diagnosis is executed and the failure diagnosis establishment flag is cleared. The fault diagnosis is stopped.

When the failure diagnosis routine is executed, first,
The purge control valve 20 and the drain valve 16 are closed, and the PCV 15 is opened, so that the space from the fuel tank 11 to the purge control valve 20 of the purge passage 19 is set as a closed space, and the tank internal pressure P detected by the internal pressure sensor 12 is reduced. The pressure change in the closed space is monitored based on the information, and it is checked whether a leak hole or the like is formed in the closed space.

As described above, in the present embodiment, PCV1
5 has reached a diagnosis start pressure P1 slightly lower than the reference control pressure Po at which the pressure adjustment operation is performed, it is determined that the diagnosis execution condition is satisfied, and the failure diagnosis is started.
Since the failure diagnosis is aborted before reaching the above condition, it is possible to accurately detect the amount of fuel vapor generated from the tank internal pressure P detected by the internal pressure sensor 12 without specially providing a sensor such as a fuel temperature sensor. Therefore, product cost can be reduced.

Further, in the present embodiment, the failure diagnosis is performed in the vicinity of the region B (pressure regulation region) where the amount of generated fuel vapor is medium, so that the failure diagnosis is started immediately after the start of the engine. As compared with the above, it is possible to make a determination in consideration of the rate of increase of the fuel temperature which is different due to the influence of the remaining fuel amount and the outside air temperature, so that the diagnosis accuracy is improved.

Further, since the failure diagnosis can be performed in the vicinity of the region B which is the pressure regulation region, the frequency of diagnosis is increased, and a highly accurate diagnosis result can be obtained.

The present invention is not limited to the above-described embodiment. For example, the internal pressure sensor 12 may be provided on the evaporation passage 13 on the upstream side of the PCV 15.

[0037]

As described above, according to the present invention,
Since there is no need to equip special sensors such as a fuel temperature sensor, product cost can be reduced, and failure diagnosis is performed in the vicinity of the pressure regulation region by the pressure regulating valve without being affected by the outside air temperature or the remaining amount of fuel. Can be started, so that not only the frequency of diagnosis is increased, but also a high-precision diagnosis result can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an evaporation purge system.

FIG. 2 is a flowchart illustrating a diagnosis execution condition determination routine;

FIG. 3 is an explanatory diagram showing a relationship between a tank internal pressure and an amount of generated fuel.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 fuel tank 11a upper space 12 internal pressure sensor (tank internal pressure detecting means) 13 evaporative fuel passage 14 canister 15 pressure regulating valve (pressure control means) 19 purge passage 20 purge control valve (purge control means) P tank internal pressure Po reference control pressure P1 Diagnosis start pressure

Claims (2)

[Claims] An evaporative fuel passage for guiding evaporative fuel remaining in an upper space in a fuel tank to a canister; a purge passage for communicating the canister with an engine intake system; a purge control means for opening and closing the purge passage; A tank internal pressure detecting means for detecting a pressure in the fuel tank, and a reference control pressure based on the tank internal pressure detected by the tank internal pressure detecting means and interposed in the evaporative fuel passage. A failure diagnosis apparatus for an evaporative purge system, comprising: a pressure adjusting means for adjusting a pressure; and a diagnosis execution condition determination means for checking whether a failure diagnosis execution condition is satisfied based on an operation state. When the internal pressure reaches a diagnosis start pressure lower than the reference control pressure, it is determined that the diagnosis execution condition is satisfied. Failure diagnosis apparatus of the purge system. 2. The evaporative purge system according to claim 1, wherein the diagnosis execution condition determination means stops the failure diagnosis when an elapsed time after the determination that the diagnosis execution condition is satisfied reaches a set time. Fault diagnosis device.